(Meth) acrylic copolymer and its production process

Abstract

There are disclosed a (meth)acrylic copolymer and its production process, wherein the (meth)acrylic copolymer has the good chelating ability and dispersibility and is excellent both in the calcium-ion-binding ability and the gelation resistance in combination, and further, the deterioration of these various performances is inhibited even in the water system of high salt concentration. The (meth)acrylic copolymer comprises a constitutional unit (a) derivative from a specific (meth)acrylic monomer (A) and a constitutional unit (b1) derivative from a specific (meth)allyl-etheric monomer (B 1 ) and has a phosphorus atom in the main chain; with the (meth)acrylic copolymer being characterized by having: a mutual ratio between the constitutional unit (a) and the constitutional unit (b1) in the specific range; a low molecular weight; and a content of phosphorus, as bonded to the copolymer, in the predetermined range; and further a gelation resistance of not more than 0.02 and a calcium-ion-binding ability of not less than 150 mgCaCO 3 /g.

What is claimed is:  
     
       1. A (meth)acrylic copolymer, which comprises a constitutional unit (a) derivative from a (meth)acrylic monomer (A) of a general formula (1) below and a constitutional unit (b1) derivative from a (meth)allyl-etheric monomer (B1) of a general formula (2) below and has a phosphorus atom in the main chain; 
       with the (meth)acrylic copolymer having:  
       a mutual ratio between the constitutional unit (a) and the constitutional unit (b1) in the range of the constitutional unit (a) 80 to 96 mol % and the constitutional unit (b1) 4 to 20 mol %; and a weight-average molecular weight in the range of 500 to 4,000; and  
       a weight P1 of phosphorus atoms as bonded to the copolymer and a weight P2 of phosphorus atoms as not bonded to the copolymer satisfy a relationship of 0.9≦P1/(P1+P2)≦1.0; and further  
       a gelation resistance of not more than 0.02 and a calcium-ion-binding ability of not less than 150 mgCaCO 3 /g;  
       wherein the general formula (1) is:                    
       (wherein: R 1  denotes a hydrogen atom or a methyl group; and X denotes a hydrogen atom, a metal atom, an ammonium group, or an organic amine group); and 
       wherein the general formula (2) is:                    
       (wherein: R 2  denotes a hydrogen atom or a methyl group; and each of Y and Z independently denotes a hydroxyl group or a sulfonic acid group (wherein the sulfonic acid group may be in the form of a monovalent metal salt, a divalent metal salt, an ammonium salt, or a salt of an organic amine group) wherein at least one of Y and Z is the sulfonic acid group). 
     
     
       2. A (meth)acrylic copolymer according to  claim 1 , wherein the mutual ratio between the constitutional unit (a) and the constitutional unit (b1) is in the range of the constitutional unit (a) 87 to 96 mol % and the constitutional unit (b1) 4 to 13 mol %. 
     
     
       3. A (meth)acrylic copolymer according to  claim 1 , wherein the total content of the constitutional unit (a) and the constitutional unit (b1) in the entire constitutional units of the copolymer is in the range of 93 to 100 mol %. 
     
     
       4. A process for producing a (meth)acrylic copolymer, which comprises the step of carrying out a copolymerization reaction of monomer components in the presence of hypophosphorous acid (salt) and a polymerization initiator to thereby produce the (meth)acrylic copolymer having a phosphorus atom in the main chain, wherein the monomer components include a (meth)acrylic monomer (A) of a general formula (1) below; 
       wherein the hypophosphorous acid (salt) begins to be supplied into the polymerization system earlier than the polymerization initiator;  
       wherein the general formula (1) is:                    
       (wherein: R 1  denotes a hydrogen atom or a methyl group; and X denotes a hydrogen atom, a metal atom, an ammonium group, or an organic amine group).